Offshore well drilling and oil storage platform



June 1, 1965 c. A. SWANLUND, JR, ETAL 3,185,130

OFFSHORE WELL DRILLING AND OIL STORAGE PLATFORM Filed April 25, 1963 3Sheets-Sheet l I-: -Z--' |3 I4----- INVENTORS! fimfifi c. A. SWANLUND,JR.

I6 32 I? c. H. SIEBENHAUSEN, JR.

FIG, BYI 5.. H514 Gad;

THEIR AGENT 3,186,180 OFFSHORE WELL DRILLING AND OIL STORAGE PLATFORMFiled April 25, 1963 June 1, 1965 c. A. SWANLUND, JR., ETAL 3Sheets-Sheet 2 FIG. 9

INVENTORSZ C. A. SWANLUND, JR.

c. H. SIEBENHAUSEN, JR. BY: H M

v THEIR AGENT June 1965 c. A. SWANLUND, JR., ETAL 3,186,180

OFFSHORE WELL DRILLING AND OIL STORAGE PLATFORM 3 Sheets-Sheet 3 FiledApril 25, 1965 FIG. I3

FIG. l4

INVENTORSZ C. A. SWANLUND, JR. C. H. SIEBENHAU FIG. 5

United States Patent 0 3,186,189 UFFfiHGRE WELL DRILLKNG AND GIL STORAGEPLATFORM Clifford A. Elwanlund, Ira, Metairie, Lea, and Christian H.Siebenhansen, .lra, Midland, Tex, assignors to Shell Oil Company, NewYork, N.Y., a corporation of Delaware FiledApr. 25, 1963, Ser. No.275,607 4 Claims. (Cl. 61-465) This invention relates to marinefoundation structures and pertains more particularly to offshoreplatforms for ,drilling oil and gas wells while providing storagefacilities for the oil produced from offshore wells. At present, onetype of a stationary platform structure commonly used for offshoredrilling or producing of wells makes use of a substructure which isconstructed in the form of a large template, preferably composed of asingle section cornprising a group of spaced hollow steel column rigidlyheld together by structural cross bracing, Piles are then driven throughthe hollow template legs or columns to the depth required for foundationsupport purposes. The piles are then fixedly secured to the template,preferably by welding and/or cement grouting and then cut off atpredetermined levels. The columns of the template are normally made of apredetermined length of pipe or casing so as to extend from the oceanfloor at an offshore drilling location to a point above the average wavelevel of the water. However in some instances, in order to minimze waveforces on the structure, the template columns and piling are terminatedbelow the normal level of the water. Mounted upon the substructureformed by the template and piles is a deck section from which drillingor producing operations are conducted. The deck section is generallyconstructed of a plurality of parallel structural trusses extendinglongitudinally and transversely of the area of the platform andintersecting each other at a plurality of points to form a generallyrectangular box-like open work structure having a surface area ofrequired dimensions for its intended use as a working platform. Thisstructural framework of the deck section then covered by a suitableflooring material upon which a conventional drilling derrick andsuitable drilling or producing equipment may be mounted. It is commonfor the deck section to have a plurality of legs extending downwardlytherefrom which are so constructed that they are in alignment with andseat within the tops of a plurality of legs of columns of the templateor in the piles installed therein.

Offshore platform structures .of the above-described type utilizing aunitary template through which piles are driven and on which a decksection is mounted have been used for several years in drilling andproducing locations on the Continental Shelf along the coasts ofLouisiana and Texas.

The well locations are generally several miles from shore.

These templates are of enormous weight and as the selected drillinglocations have been in deeper and deeper water it has been found to beimpossible at some water depths to transport and install an ofifshoreplatform structure .of the template type because of the great size andweight of the template. Merely dividing the template into a number ofsections that are installed separately and connected above sea level atthe drilling location is expensive and also in deep water exactalignment of the various segments of the structure is difficult. Also,there is no underwater continuity of a sectionalized structure of thistype thus reducing its ability to withstand forces due to wind and waveaction and reducing the load-carrying capacity.

For installing an offshore platform structure in a deep water location,say 300 feet, it has been suggested that the platform be sectionalizedwith each section being provided with buoyancy tanks so that thesections may be floated separately to the assembly location. It is thenproposed to drive four legs into the ocean floor in spaced apartrelationship, lift each fioatable platform section out of the water andlower it over the legs and subsequently flood the buoyancy tanks tocause the platform section to sink to the bottom while sliding along thefour legs as guide members. It may be seen that this arrangement hasconsiderable drawbacks as it is almost impossible to accurately spacethe lower ends of the 300 foot piles in the ocean floor without the useof some sort of template.

Another suggested scheme for buoyant deepwater offshore structuresinvolves the use of large diameter vertical legs two of which supportthe structure while being transported to the site. In this scheme oiland gas wells may be drilled through the vertical legs. An objection tothis scheme is the fact that the columns and consequently the piling arenot battered; and therefore, the large lateral wind and wave forcescannot be resisted as well as they would be resisted by battered pilesand columns.

It is therefore a primary object of this invention to provide anoffshore drilling platform capable of being fabricated on land andtransported to a deep water location where it is subsequently erectedand positioned on the ocean floor as a unit.

A further object of the present invention is to provide an offshoreplatform structure provided with sufiicient buoyancy so that thestructure may be floated to a water location.

Another object of the present invention is to provide a buoyant platformstructure having superior lateral stability characteristics in that thetemplate columns and piles are inclined on a batter.

A further object of the present invention is to provide a buoyantplatform structure adapted to be erected at a deepwater location fromwhich drilling operations can be carried out with the oil produced fromany underwater wells being stored by the platform structure.

Still another object of the present invention is to provide a buoyantoffshore platform structure adapted to be erected in deepwater locationsby presently available equipment.

These and other objects of this invention will be understood from thefollowing description taken with reference to the drawing, wherein:

FIGURE 1 is a longitudinal view showing the platform structure of thepresent invention positioned at an offshore location with the decksection of the platform being provided with well production handlingfacilities;

FIGURE 2 is a longitudinal view of the upper portion of a platform ofFIGURE 1 wherein the deck section is provided with storage shed orliving quarters;

FIGURE 3 is a longitudinal view of the upper section of the platformstructure of FIGURE 1 wherein the deck section is equipped with aderrick while drilling operations are being carried out;

FIGURE 4 is a cross-sectional view along the line 4-4 of FIGURE 2;

FIGURE 5 is an isometric view diagrammatically showing one arrangementof a production facility for handling production fluid from wells andtransferring it into and out of the central storage tank of the platformstructure of FIGURE 1;

FIGURE 6 is a cross-sectional view taken in longitudinal projection ofthe lower end of a template column with a removable cover plate;

FIGURES 7 through 14 are schematic views illustrating the sequentialsteps of one manner of towing the platform structure of the presentinvention to a selected offshore location, unloading the platformstructure from a barge, floating the platform structure horizontally inthe water with hoses connected for flooding the buoyancy tanks of thestructure, upending the platform structure and setting it in place onthe ocean floor, installing the deck portion of the platform structureafter driving piles through the legs of the structure, drilling wellsfrom the platform structure into the ocean floor while employing asecond structure adjacent the first platform for storing equipment andserving as living quarters, drilling wells into the ocean floor from thesecond platform structure, and finally producing the wells of bothstructures with one of the structures being provided with productionfacilities in order to carry out operations such as separating the oil,gas and water phases of the production fluid and metering and storingthe oil.

Referring to FIGURE 1 of the drawing, an offshore platform structure inaccordance with the present invention is shown as comprising a pluralityof long substantially vertical legs 11 and 12 in spaced relationshipwith each other and interconnected by cross bracing members 13, 14 and15 arranged in any suitable configuration, preferably in a manner toprovide the greatest rigidity to the structure. It is preferred that thetubular legs 11 and 12 slant downwardly and outwardly from a center linethrough the platform structure so that the base of the structureencloses an area greater than the top of the platform structure therebygiving the platform structure greater stability. Although only two legs11 and 12 appear in FIGURE 1, it is to be understood that the platformstructures comprise at least three and preferably four legs of a lengthgreater than the water depth at which they are located and cross-bracedtogether in a configuration with a closed periphery. The legs 11 and 12are preferably open throughout their entire length so that piles 16 and17 can be driven through them into the ocean floor 18. Prior to drivingthe piles 16 and 17 through the legs 11 and 12, at least one of the legsand preferably all of the legs are closed in a fluid-tight manner atboth ends by suitable removable closure means well known to the art, forexample as by welding a knock-out plate 19 (FIGURE 6) over the end ofthe leg. The plate 19 would be driven out when a pile was driven throughthe leg. The closed legs form auxiliary buoyancy tanks which aid infloating the platform structure. For a platform 300 feet high, the legsmay be from 3 to feet in diameter.

Positioned within the center of the platform structure a large diametertank, for example 20 to feet in diameter, which extends longitudinallywithin the structure substantially the length of the legs 11 and 12 andbeing cross-braced thereto so that it is rigidly supported. The top ofthe tank 21 is positioned a distance below the surface of the ocean 22 adistance sufficient to be below the most violent wave action, thusreducing the wave forces imposed upon the platform structure.

Extendinglongitudinally through the tank 21 are a plurality ofrelatively large diameter conduits 23, 24 and 25 or well casing whichextend through the ends of the tank in a fiuidtight manner. The wellconduits 23, 24

and 25 may be closed at both ends in a manner similar to the legs anddescribed with regard to FIGURE 6 so as to serve as auxiliary buoyancytanks for the platform structure. The main buoyancy tank in thestructure is the central tank 21 which is provided with port means 26and 27 at the upper and lower ends thereof one of which is adapted to beconnected to a hose for pumping water in the tank when the structure issunk into place on the ocean floor while allowing air to leave throughthe other port 26 at the top of the tank while water is being pumpedinto the bottom of the tank through a hose 28 (FIGURE 9) connected tothe port 27. As an alternative flooding method sea water is allowed toflow into the cylinder and controlled by exhausting air at the topthrough a valve. If desired, the tank 21 (FIGURE 1) may be provided witha transverse plate member 29 which divides the tank 21 but not the wellconduits 23, 24 and 25 into upper and lower fluidtight sections. In theevent that the tank 21 is divided into upper and lower fiuidtightsections, the upper section would be provided with ports 26 and 2701while the lower section was provided with ports 26a and 4 27 wherebyboth tanks could be selectively flooded and/ or evacuated if necessary.Additionally, if necessary, instead of employing a horizontal transverseplate 29 the plate member could extend vertically through the tank todivide the tank into at least two longitudinal fluidtight sections whichcould be independently flooded.

The well conduits 23, 24 and 25 are of a diameter suflicient so thatdrilling operations can be carried out through them with well casings31, 32 and 33 being subsequently extended through the well conduits 23,24 and 25 and extending up to the lower deck 34 where they would beclosable in a normal manner as by valve assemblies in the form ofChristmas trees 35, 36 and 37.

Mounted on the upper ends of legs 11 and 12 of the platform structureIt) is a deck unit 38 comprising a plurality of vertical legs 41 and 42interconnected as necessary by cross bracing members 43 and 43a andspaced apart sufficiently to mate with the top of the legs 11 and 12 ofthe platform structure. The legs 41 and 42 sup port one or more decks 34and 44 which in turn support the necessary equipment normally associatedwith a production facility at an offshore location, such for example asseparators 45 and 56, pump 47 and storage shed and living quarters 43.It is to be understood as described hereinbelow with regard to FIGURE 5,the production handling equipment such as the separators 45 and 46 areinterconnected by means of conduits with the central tank 21 of theplatform structure, or with the several independent sections of the tankif it is divided into more than one section. In FIGURE 2, the identicalplatform structure described with regard to FIGURE 1 is shown exceptthat the deck unit 38 is provided with a living quarters building 49.The upper ends of the well conduits 23, 24 and 25 (FIGURE 1) may beprovided with funnel-shaped openings 50, 51 and 52 at their upper ends(FIGURE 2) to aid in inserting pipe therethrough.

In FIGURE 3 the identical platform structure of FIG- URE 1 isillustrated with the top thereof being provided with a derrick 53 havinga fall line system 54 and a traveling block 55. These elements togetherwith a hoist 56 and associated auxiliary drilling equipment suspend adrill string 57 which extends down through a rotary table 58 and one ofthe well conduits of the tank 21. An auxiliary vessel 60 is shown asbeing moored along the side of the platform structure 10.

A cross section of the buoyancy and storage tank 21 is shown in greaterdetail in FIGURE 4. The tank 21 may be centrally positioned within theplatform structure by means of support members 61 and 62, which may inthe case of support member 62 extend entirely through the tank 21 togive greater rigidity to the tank. In addition to well conduits 23, 24and 25, the tank 21 in FIGURE 4 is shown as being provided with threemore well conduits 63, 64 and 65. The number of well conduits providedin the tank 21 would depend upon the size of the tank, the number ofwells to be drilled from the platform structure, and the spacing desiredbetween each of the wells. At spaced levels along the tank 21 the wellconduits 23, 24 and 25 are preferably reinforced by support bars 66 and67 to which they are welded.

In accordance with the present invention, the platform structure 10(FIGURE 1) is fabricated on land and then either floated in the waterand towed to the selected offshore location, or placed on a barge 68(FIGURE 7) which is towed to the desired location by means of a tug 69.In the event that the barge 68 is employed, the barge is preferablyprovided with skid beams or a sloping skidway 70 on which the platformstructure 10 is positioned and secured thereto. On arriving at theselected location, another vessel 60 may be employed to help pull theplatform structure 10 off the skidway 70 of the barge 68 as shown inFIGURE 9, or then it may be pulled into the water by a block and tackleand hoist located on the barge 68. With the platform structure pulledinto the water as illustrated in FIGURE 9, the buoyancy of the centralstorage tank 21 is suflicient to float the platform structure in thewater. Since there may be a tendency for the platform structure to rollin the water on the longitudinal axis of the tank 21, at least one ofthe legs is preferably sealed top and bottom as previously described soas to serve as an auxiliary buoyancy tank. Thus, in the event that theplatform structure 21 was to roll in the water, it would only roll untilthe buoyant leg came in contact with the surface of the water at whichtime the buoyant leg would serve as an outrigger and stabilize theplatform structure against roll. A preferred arrangement is to have allof the legs buoyant to reduce possibility of the structure rolling.

With the platform structure shown in the position in FIGURE 9, Waterwould be pumped through hose 23 into the bottom of the tank 21 or thetank would be otherwise flooded until the platform structure settledbottom first to the ocean floor as shown in FIGURE 10, piles would thenbe driven through the legs of the platform structure and if desiredcemented to the ocean floor. Subsequently, the tops of the piles wouldbe cut off at the tops of the legs of the platform structure andpreferably secured thereto as by welding. The deck section 38 would thenbe lowered into place on top of the upper end of the platform structure10, as by means of a crane on vessel 60, as shown in FIGURE 11.

In FIGURE 12 two identical platform structures in accordance with thepresent invention are shown as being positioned on the ocean floor withpiles having been driven through their legs and deck section provided ontheir upper ends. Platform structure 19a is provided on its upper deckwith living quarters 49 or a storage shed that is connected to the otherplatform structure by means of a walkway 70. Drilling operations arebeing carried out on platform 10 from the derrick 53 mounted thereon.

After having drilled the desired number of wells from platform structure10 (FIGURE 13) the derrick 53 was moved to platform structure 10a tocarry on drilling operations while the living quarters or storagefacility 49 were moved to platform structure 10. After completing thescheduled drilling from both platforms 10 and 10a, a production facilitysuch as one employing separators 45 and 4-6 is mounted on the top of oneof the platforms, in this instance platform 19a, while production fluidis piped from the wells drilled from platform 14) through conduit 71extending between the two platforms 1t? and 19a.

One form of a production handling facility adapted to be mounted on thedeck unit of a platform structure in accordance with the presentinvention is shown in FIG- URE 5 schematically with the legs andcross-bracing members of the platform cut away from the central storageand buoyancy tank 21 and with the well casings 23, 24 and 25 (FIGURE 1)omitted from the tank 21 (FIG- URE 5). The illustrated productionfacility in FIGURE 5 utilizes sea water displacement of oil within thestorage tank 21 so that the tank is full of liquid at all times andhence not subjected to the stresses of an underwater tank which ispartially empty.

With the oil floating on top of the water within the tank, the tank isprovided with an oil discharge line 73 from the top thereof whichextends upwardly through deck 34 and is adapted to be closed by a valve74. This line may be 12 inches in diameter, for example, and beyondvalve 7 4 is provided with a flexible hose 75 adapted to extend to anoil barge moored alongside the structure. Production fluid from one ofthe wells is received through conduit 76 and passes through an oil, gasand water separator 77 so that only oil is discharged through conduit'78 and down pipe 79-73 into the top of the tank 21. In the event thatoil was being discharged from the tank 21 into a tanker alongside (notshown) a control valve 80 in the conduit 79 would be closed so that theflow of oil from the separator 77 and through line 78 would be directedthrough a side conduit 81 into a temporary oil storage tank 82.

In order to discharge oil from the storage tank 21 one or more suctionpumps 83 and 84 are provided with suction tubes 85 and 86 whose lowerends extend down below the surface of the water 22. The discharge of thepumps 83 and 84 is normally through open conduits 87 and 88 into a waterstorage tank 89 having an overflow line 90 to control the'head of fluidand hence limit the pressure being applied to the storage tank 21. Thewater discharge line 91 from the water tank 89 is normally open at alltimes and extends to the bottom of the storage tank 21. can be bypassedby opening one of the norm-ally closed valves 92 or 93 in the dischargeline from pumps 83 and at so that water is pumped directly down line 91into the tank 21.

A third line 94 extending to the bottom of the tank 21 is preferablyprovided with the flow therethrough being controlled by normally closedvalve 95. This is a purge line which is employed when it is desired toclean out sediment from the bottom of tank 21. In cleaning sediment fromthe tank 21, valve 95 would be open and water would be pumped from oneof the pumps 84 and 83 down water line 91 to the bottom of the tank withthe water then being discharged up purge line 94, through valve 95 tothe sea.

By utilizing a single storage tank in the center of the offshoreplatform structure through which wells may be drilled, the largeststorage capacity of oil is provided with a minimum surface being exposedto lateral forces tending to tip the platform structure over. At thesame time it is possible to employ batter legs at the corners of thestructure thus giving the structure much more stability than could berealized by straight legs. It is only by employing this combination ofelements that it is possible to provide the greatest stability for astructure of any given height while at the same time being able to startdrilling wells in a vertical direction and subsequently providingstorage capacity for the produced oil from the wells drilled from theplatform of the present invention.

We claim as our invention:

1. An offshore platform structure for extending from the bottom of abody of water to above the surface of the water comprising,

a plurality of tubular legs of 'a length greater than the water depthand cross-braced together in a framework having a configrn'ation with aclosed periphery, said tubular legs slanting downwardly and outwardlyfrom a center line through the platform structure whereby the base ofthe structure encloses a larger area than the top of said structure,

a large-diameter tank extending longitudinally substantially the lengthof the legs of the structure and crossbraced thereto in the center ofthe structure entirely within the framework formed by said legs, the topof the tank being below the top of said structure a distance sufficientto be below the most violent wave action when the structure is inposition on the bottom of the body of water,

said tank being closed and having a buoyancy sufficient to float theentire structure in a body of water, the interior of the tank being opento movement of fluid in both directions substantially throughout itsentire length,

at least one of the tubular legs being closed at the ends thereofproviding an outrigger buoyancy tank in contact with the waterpreventing rotation of said platform structure about its longitudinalaxis when floating in water,

a plurality of longitudinally-extending conduits carried in said tankand extending the length thereof,

removable closure means closing both ends of said conduits in afluidtight manner so that the conduits form auxiliary buoyancy chambers,

said conduits being of a diameter suflicient to carry out well drillingoperations therethrough,

If desired, the water storage tank 89 port means through the wall ofsaid tank for flooding said tank from the lower end thereof therebycausing the tank and structure to tilt bottom down to a vertioalposition within a body of water, and

first conduit means for admitting oil to said tank and second conduitmeans for admitting water to said tank to displace the oil therefrom.

2. The apparatus of claim 1 wherein the legs are closed top and bottomby removable closure means.

3. The apparatus of claim 1 wherein the centrallylocated tank of saidplatform structure is secured to said structure in a manner such thatthe upper end of the tank floats slightly higher out of the water thanthe lower end of the tank when said tank is in a substantiallyhorizontal position.

4. The apparatus of claim 1 wherein the centrally- References Cited bythe Examiner UNITED STATES PATENTS Kuss et 'al. 6146.5 X

Schaufele 6146.5 Crake 6l-46.5 X

Newcomb 61-46.5 Sandberg 6146.5

15 EARL J. WITMER, Primary Examiner.

JACOB SHAPIRO, Examiner.

1. AN OFFSHORE PLATFORM STRUCTURE FOR EXTENDING FROM THE BOTTOM OF ABODY OF WATER TO ABOVE THE SURFACE OF THE WATER COMPRISING, A PLURALITYOF TUBULAR LEGS OF A LENGTH GREATER THAN THE WATER DEPTH ANDCROSS-BRACED TOGETHER IN A FRAMEWORK HAVING A CONFIGURATION WITH ACLOSED PERIPHERY, SAID TUBULAR LEGS SLANTING DOWNWARDLY AND OUTWARDLYFROM A CENTER LINE THROUGH THE PLATFORM STRUCTURE WHEREBY THE BASE OFTHE STRUCTURE ENCLOSES A LARGER AREA THAN THE TOP OF SAID STRUCTURE, ALARGE-DIAMETER TANK EXTENDING LONGITUDINALLY SUBSTANTIALLY THE LENGTH OFTHE LEGS OF THE STRUCTURE AND CROSSBRACED THERETO IN THE CENTER OF THESTRUCTURE ENTIRELY WITHIN THE FRAMEWORK FORMED BY SAID LEGS, THE TOP OFTHE TANK BEING BELOW THE TOP OF SAID STRUCTURE A DISTANCE SUFFICIENT TOBE BELOW THE MOST VIOLENT WAVE ACTION WHEN THE STRUCTURE IS IN POSITIONON THE BOTTOM OF THE BODY OF WATER, SAID TANK BEING CLOSED AND HAVING ABUOYANCY SUFFICIENT TO FLOAT THE ENTIRE STRUCTURE IN A BODY OF WATER,THE INTERIOR OF THE TANK BEING OPEN TO MOVEMENT OF FLUID IN BOTHDIRECTIONS SUBSTANTIALLY THROUGHOUT ITS ENTIRE LENGTH, AT LEAST ONE OFTHE TUBULAR LEGS BEING CLOSED AT THE ENDS THEREOF PROVIDING AN OUTRIGGERBUOYANCY TANK IN CONTACT WITH THE WATER PREVENTING ROTATION OF SAIDPLATFORM STRUCTURE ABOUT ITS LONGITUDINAL AXIS WHEN FLOATING IN WATER, APLURALITY OF LONGITUDINALLY-EXTENDING CONDUITS CARRIED IN SAID TANK ANDEXTENDING THE LENGTH THEREOF, REMOVABLE CLOSURE MEANS CLOSING BOTH ENDSOF SAID CONDUITS IN A FLUIDTIGHT MANNER SO THAT THE CONDUITS FORMAUXILIARY BUOYANCY CHAMBERS, SAID CONDUITS BEING IN A DIAMETERSUFFICIENT TO CARRY OUT WELL DRILLING OPERATIONS THERETHROUGH, PORTMEANS THROUGH THE WALL OF SAID TANK FOR FLOODING SAID TANK FROM THELOWER END THEREOF THEREBY CAUSING THE TANK AND STRUCTURE TO TILT BOTTOMDOWN TO A VERTICAL POSITION WITHIN A BODY OF WATER, AND FIRST CONDUITMEANS FOR ADMITTING OIL TO SAID TANK AND SECOND CONDUIT MEANS FORADMITTING WATER TO SAID TANK TO DISPLACE THE OIL THEREFROM.